ABSTRACT Pulmonary immaturity, specifically hyaline membrane disease, is a major factor in the morbidity and mortality associated with premature birth. The disease is related to the lack of synthesis and secretion of surfactant from the Type II cells. The proposed study is designed to test the hypothesis that surfactant release from Type II pulmonary epithelial cell is mediated hormone stimulated by c-AMP synthesis, c-AMP dependent protein kinase activation and the subsequent phosphorylation of specific cellular proteins which in turn alter intracellular Ca2+ homeostasis leading to surfactant release. Secondly it is proposed that a dramatic maturation of this response system, required for surfactant release and for the ability of the newborn to adapt to extrauterine life, occurs in the perinatal period. It is predicted that the maturation of the response system is also hormonally mediated and that there exists the potential for therapeutic regulation of the c-AMP dependent system in the fetus prior to birth. The study will utilize short term cultures of isolated, purified Type II pneumocytes from adult rat lung. Systematic studies to demonstrate Beta-adrenergic receptors, PGE1 and catecholamine mediated c-AMP synthesis, c-AMP dependent protein kinase activation and c-AMP dependent protein phosphorylation reactions will be performed to identify the possible cellular mechanisms involved in surfactant release responses to these agents. Identification and characterization of the above activities will be performed in the adult Type II cells and correlated with the characteristics of surfactant release. Following a clarification of the above regulatory events in the adult Type II cell, more difficult studies to determine the development and maturation of this system in fetal lung will be performed. These latter experiments will utilize short term retal rat lung explant culture in serum free medium to determine possible humoral regulation of the maturation of the various components of the cAMP response system. Finally the proposal will attempt to prepare fetal Type II cells for similar studies of the maturation of hormone sensitive surfactant release mechanisms. The overall objective of the study is to determine the possible cellular mechanisms involved in the maturation of surfactant release which may play a role in the pathogenesis of hyaline membrane disease and other respiratory problems of the premature born infant.